This invention relates to hydraulic circulation systems for cleaning holes being drilled in rock and earth, as in the oil industry. More particularly, the present invention relates to a pickup tube mounted on a rock bit in a position which improves the removal of cuttings by increasing horizontal flow at the bottom of such a hole.
While substantial advances have been made in rock bit technology relating to virtually every element of such bits, one of the remaining limiting characteristics, particularly in bits having three or fewer cones, is the tendency of the cutting teeth to recut or regrind rock already cut away from the bottom of the hole. This tendency is due primarily to the inability of the drilling fluid circulation system to adequately sweep chips from the bottom of the hole before successive cones capture and recrush them.
To some extent, these problems have been reduced in large diameter rock drilling bits, such as those used for drilling mine shafts. Such bits, although plagued with other problems because of their size, nevertheless permit the strategic placement of nozzles and extended collection tubes for efficient chip removal from the hole bottom. Small gage holes do not permit such freedom of location of flow controlling members. Nevertheless, the extensive use of rock bits having three or fewer cones in relatively small gage holes in the oil industry has led to numerous attempts to improve the chip removal system in such bits. None of these attempts have been entirely satisfactory.
One of the limiting requirements is the construction of a three cone bit itself, since virtually all of the space at the bottom of the hole is occupied by drill bit cutting faces. A further limitation is the high pressures and flow rates of the drilling fluid itself, which prohibits flow conduits which would induce radical direction changes in the fluid. Thus, prior systems which attempted to change the course of the drilling fluid at the bottom of the hole to induce an upward flow direction from upturned nozzles have been found to be impractical, since fluid, particularly when abrasive, will literally destroy nozzles which attempt to turn the 90+ degrees required for upward flow.
Virtually all systems for altering the hydraulic drill fluid flow characteristics have concentrated on the nozzles which direct a powerful stream of drilling fluid toward the hole bottom. Once removed by this stream, the cut chips are permitted to escape (generally around the annulus between the bit and the walls of the drilled hole), without particular concern regarding the outgoing flow pattern. In many instances this outgoing flow places a large percentage of the chips in a location which is likely to cause regrinding of the chips by the gage surfaces of the cones, limiting the life of the gage surfaces.
Some prior art has attempted to place all input nozzles on one side of the hole, and to increase flow clearances on the other side of the hole. These systems, however, because of the tendency of the drilling fluid to flow upward after impact with the hole bottom, have met with only limited success.
Thus, the prior art, in concentrating on improving the nozzle portion of the drilling fluid circulation system, has been faced with the continuing requirement that radical flow direction changes not be included in the pressure fluid passages, so that only a limited degree of horizontal flow could be induced at the bottom of the drilled hole. This requirement, together with the severe space limitations in three cone bits, has thus far prevented the prior art from generating large horizontal flow vectors.